Gestational diabetes mellitus

Gestational diabetes mellitus (GDM) is diabetes mellitus that develops in women for the first time in pregnancy. Pregnancy increases the risk of developing diabetes because of placental hormones. These placental hormones increase glucose levels and the body’s resistance to insulin, which is a hormone important for the control of blood glucose. GDM usually starts in the second or third trimester. 

If well-controlled, most women diagnosed with GDM will have normal pregnancies and babies. However, if not well-controlled, GDM has potential risks for both mother and baby. It is therefore important to diagnose and treat GDM optimally to reduce these risks.

GDM usually does not give rise to any symptoms, but is detected by a blood test called an oral glucose tolerance test (OGTT) done in the second trimester. 

When GDM goes undetected or untreated, the developing foetus may be larger than normal, or there might be more “water” (amniotic fluid) in the womb than normal. 

When blood glucose levels are very high, symptoms such as increased thirst, increased urination or weight loss may occur.

Steps can be taken to reduce the risk of having GDM both before and during pregnancy. This is important, especially if you have risk factors for GDM, or if you have had GDM during a previous pregnancy.

Having a healthy, balanced diet and regular exercise before and during pregnancy is important. These steps will help to achieve and maintain a healthy weight before becoming pregnant. A body mass index (BMI) of 18.5 – 22.9 kg/m2 is considered to be within the healthy range. 

Risk factors for GDM include:

Although the risk of GDM is higher in certain groups of women, it can happen to any woman in her pregnancy. In Singapore, all pregnant women will be offered screening for GDM with an oral glucose tolerance test (OGTT) between 24 and 28 weeks of pregnancy.

If you have had GDM before, having glucose in the urine, or symptoms suggestive of diabetes, the OGTT will be performed earlier in pregnancy and repeated again at 24 – 28 weeks if the first test was normal. 

Detection of GDM is important so that appropriate treatment can be given to reduce the risks to the pregnancy.

When you have GDM, you will be under the care of a specialist healthcare team comprising obstetricians, endocrinologists, specialised nurses and dieticians.

GDM usually improves with lifestyle measures such as healthy eating and exercise.

Despite best efforts at achieving a healthy lifestyle, some women need to take tablets or insulin injections to control their glucose levels.

You will be taught how to use a glucometer to monitor your sugar levels at different time points within the day, and how to self-inject insulin if you need insulin therapy. 

At every doctor’s visit, a blood test (HbA1c) will be done to measure your average blood glucose level. Blood pressure checks, urine tests, and ultrasound scans to monitor your baby’s growth will also be done to ensure that the pregnancy is a healthy one.

Your specialist team will give you advice about the timing and type of delivery. During labour, blood glucose levels will be monitored frequently and some women may require an insulin drip for optimal control.

After delivery, most patients who require tablets or insulin injections during pregnancy are able to stop their medications. However, some women may have persistent diabetes after pregnancy. Therefore, a repeat OGTT is needed about 6 – 12 weeks after delivery to check if the GDM has resolved.